1. Field of the Invention
The present invention relates to a lamp unit of a vehicle headlamp, and in particular to a projector-type lamp unit that uses a light-emitting element such as a light-emitting diode as a light source.
2. Related Art
Recently, in vehicle headlamps, light-emitting elements such as light-emitting diodes become to be used as light sources.
For example, disclosed in JP-A-2003-317513 is a so-called projector-type lamp unit provided with a projection lens arranged on an optical axis extending in a front/rear direction of a vehicle, a light-emitting element arranged upward behind a rear focal point of the projection lens and in proximity to the optical axis, and a reflector for reflecting light from the light-emitting element in forward direction toward the optical axis.
Further, disclosed in JP-A-2005-044809 and JP-A-2005-108554 are projector-type lamp units where first and second light source units are arranged behind a projection lens.
In the lamp unit described in JP-A-2005-044809 and JP-A-2005-108554, the first light source unit includes a first light-emitting element arranged upward in proximity to an optical axis, a first reflector for reflecting light from the first light-emitting element in forward direction toward the optical axis, and a straight advancement interrupting member for interrupting part of the reflected light from the first reflector, the straight advancement interrupting member arranged so that its upper end edge passes near the rear focal point of the projection lens. The second light source unit includes a second light-emitting element arranged downward in proximity to the optical axis and a second reflector for reflecting light from the second light-emitting element in forward direction toward the optical axis.
When the first light source unit is turned on, a low beam light distribution pattern having a cutoff line at the upper end is formed. When the second light source unit is additionally turned on, a high beam additional light distribution pattern extending upward from a cutoff line is additionally formed to form a high beam light distribution pattern.
In the projector-type lamp unit described in JP-A-2005-044809, JP-A-2005-108554, it possible to switch between high beams and low beams by turning on/off the second light source unit.
However, a high beam additional light distribution pattern formed when the second light source unit is turned on is formed only above a cutoff line. This does not enhance the luminosity of the region near the cutoff line in the high beam light distribution pattern. As a result, the high beam light distribution pattern remains poor in terms of long-distance visibility.